Saturn's turbulent F ring

As our abilities to utilise high performance computing to theoretically probe many astrophysical systems increases, a genuine need to relate to real systems becomes ever more important. Here, Saturn s rings can be used as a nearby laboratory to investigate in real time many astrophysical processes. One such system is the narrow F ring and its interaction with its inner shepherd moon Prometheus. Through numerical modelling and direct observations of the in-situ spacecraft Cassini we find new and exciting dynamics. These might help explain some of the asymmetries witnessed in the distribution of embedded moonlets and azimuthal ring brightness known to exist within the F ring. Spatially we find asymmetry in the Prometheus induced channel edges with regards to density, velocity and acceleration variations of ring particles. Channel edges that show fans (embedded moonlets) are also the locations of highly localised increases in densities, velocity and acceleration changes where opposing edges are considerably less localised in their distribution. As a result of the highly localised nature of the velocity and acceleration changes chaotic fluctuations in density were witnessed. However, this could seek to work in favour of creating coherent objects at this channel edge as density increases were significantly large. Thus, density here had a greater chance of being enhanced beyond the local Roche density. Accompanied with these dynamics was the discovery of a non-zero component to vorticity in the perturbed area of the F ring post encounter. By removal of the background Keplerian flow we find that encounters typically created a large scale rotation of ~10,000 km^2. Within this area a much more rich distribution of local rotations is also seen located in and around the channel edges. Although the real F ring and our models are non-hydrodynamical in nature the existence of a curl in the velocity vector field in the perturbed region could offer some interesting implications for those systems that are gas rich

A Detailed Numerical Analysis of Asymmetrical Density Distribution in Saturn's F ring During an Encounter with Prometheus

Saturn's rings, reminiscent of an early Solar System present a unique opportunity to investigate experimentally some mechanisms thought to be responsible for planet and planetesimal formation in protoplanetary discs. Here we extended the comparison of our numerical models of Prometheus encountering the F ring employing non-interacting and interacting particles. Higher resolution analysis revealed that the density increases known to exist at channel edges is more complex and localised than previously thought. Asymmetry between density increases on channel edges revealed that the channel edge facing way from Prometheus to be the most stable but with lowest maximum increases. However, on the channel edge facing Prometheus the interacting model showed large chaotic fluctuations in the maximum density of some clumps, much larger than those of the other channel. The likely cause of this asymmetry is a variance in localised turbulence introduced into the F ring by Prometheus. High resolution velocity dispersion maps showed that there was a spatial link between the highest densities and the highest velocity dispersions in the interacting model. Thus suggesting that the high velocity dispersion we see is the reason for the observed inhomogeneous distribution of fans (evidence of embedded moonlets) on some of the channel edges facing Prometheus

Gravitational vortices and clump formation In Saturn's F ring during an encounter with Prometheus

Saturn rings are most beautiful and dynamic places in the solar system, consisting of ice particles in a constant battle between the gravitational forces of Saturn and its many moons. Fan, spiral, propellers, moonlets and streamer-channels observed by CASSINI in the F-ring have been attributed to encounters by Prometheus on the F ring, with investigations of optical thickness revealing large populations of transient moonlets. Taking into account gravitational interaction between particles and a multi-stranded F-ring structure we show that Prometheus' encounters create rotational flows, like atmospheric vortices and the self-gravity enhances the accelerated growth and size of moonlets. Vortex patches form caustics, which is a primary cause of the transient particle density clumps of 20 km width and 100 km length, and they are elongated to cover an area of 1600 km by 150 km, which may eventually combine into a vortex sheet

Prometheus induced vorticity in Saturn’s F ring

Saturn’s rings are known to show remarkable real time variability in their structure. Many of which can be associated to interactions with nearby moons and moonlets. Possibly the most interesting and dynamic place in the rings, probably in the whole Solar System, is the F ring. A highly disrupted ring with large asymmetries both radially and azimuthally. Numerically non-zero components to the curl of the velocity vector field (vorticity) in the perturbed area of the F ring post encounter are witnessed, significantly above the background vorticity. Within the perturbed area rich distributions of local rotations is seen located in and around the channel edges. The gravitational scattering of ring particles during the encounter causes a significant elevated curl of the vector field above the background F ring vorticity for the first 1–3 orbital periods post encounter. After 3 orbital periods vorticity reverts quite quickly to near background levels. This new found dynamical vortex life of the ring will be of great interest to planet and planetesimals in proto-planetary disks where vortices and turbulence are suspected of having a significant role in their formation and migrations. Additionally, it is found that the immediate channel edges created by the close passage of Prometheus actually show high radial dispersions in the order ~20–50 cm/s, up to a maximum of 1 m/s. This is much greater than the value required by Toomre for a disk to be unstable to the growth of axisymmetric oscillations. However, an area a few hundred km away from the edge shows a more promising location for the growth of coherent objects

On the tidal environment of an outwardly migrating F ring

Saturn’s F-ring is a unique narrow ring that lies radially close to the tidally disruptive Roche limit of Saturn for water ice. Significant work has been done on the system that shows it to be one of the most dynamic places in the Solar System. Aggregates fortunate enough to form constantly battle against the strong tidal forces of Saturn and the nearby moons Prometheus and Pandora, which act to gravitationally stir up ring material. Planetary rings are also known to radially spread, with the outer ring edge migrating outwards. As the F ring lies at the edge of the main rings, we investigate the effect of an outwardly migrated F ring and its interaction with Prometheus. For each model with decreasing local tidal environment, an increase in maximum number density of particles at the channel edges is observed. In the same locations as particles with maximum number densities, radial velocity dispersion's are observed to fall below escape velocities of a 150m icy moonlet (<10 cm s^(-1)), and are gravitationally unstable with Toomre parameters Q<2. Additionally, in locations of the ring where Q<2 is observed, more particles are seen to fall below or close to critical values as the radial location of the ring increases

Mapping the location of terrestrial impacts and extinctions onto the spiral arm structure of the Milky Way

High density regions within the spiral arms are expected to have profound effects on passing stars. Understanding of the potential effects on the Earth and our Solar System is dependent on a sufficient dynamic model of arm passage. Using a novel combination of data we derive a model of the timings of the Solar System through the spiral arms and the relationship to arm tracers such as methanol masers. This reveals that asteroid/comet impacts are significantly clustered near the spiral arms and within specific locations of an average arm structure. The end-Permian and end-Cretaceous extinctions are shown to be located within a small star formation region in two different arms. The start of the Solar System greater than 4.5 Ga occurs in the same region in a third arm. The model complements geo-chemical data in determining the relative importance of extra-Solar events in the diversification and extinction of life on Earth

Sampling molecular conformations and dynamics in a multiuser virtual reality framework

Copyright © 2018 The Authors, some rights reserved. We describe a framework for interactive molecular dynamics in a multiuser virtual reality (VR) environment, combining rigorous cloud-mounted atomistic physics simulations with commodity VR hardware, which we have made accessible to readers (see isci.itch.io/nsb-imd). It allows users to visualize and sample, with atomic-level precision, the structures and dynamics of complex molecular structures “on the fly” and to interact with other users in the same virtual environment. A series of controlled studies, in which participants were tasked with a range of molecular manipulation goals (threading methane through a nanotube, changing helical screw sense, and tying a protein knot), quantitatively demonstrate that users within the interactive VR environment can complete sophisticated molecular modeling tasks more quickly than they can using conventional interfaces, especially for molecular pathways and structural transitions whose conformational choreographies are intrinsically three-dimensional. This framework should accelerate progress in nanoscale molecular engineering areas including conformational mapping, drug development, synthetic biology, and catalyst design. More broadly, our findings highlight the potential of VR in scientific domains where three-dimensional dynamics matter, spanning research and education

Evolvable Neuronal Paths: A Novel Basis for Information and Search in the Brain

We propose a previously unrecognized kind of informational entity in the brain that is capable of acting as the basis for unlimited hereditary variation in neuronal networks. This unit is a path of activity through a network of neurons, analogous to a path taken through a hidden Markov model. To prove in principle the capabilities of this new kind of informational substrate, we show how a population of paths can be used as the hereditary material for a neuronally implemented genetic algorithm, (the swiss-army knife of black-box optimization techniques) which we have proposed elsewhere could operate at somatic timescales in the brain. We compare this to the same genetic algorithm that uses a standard ‘genetic’ informational substrate, i.e. non-overlapping discrete genotypes, on a range of optimization problems. A path evolution algorithm (PEA) is defined as any algorithm that implements natural selection of paths in a network substrate. A PEA is a previously unrecognized type of natural selection that is well suited for implementation by biological neuronal networks with structural plasticity. The important similarities and differences between a standard genetic algorithm and a PEA are considered. Whilst most experiments are conducted on an abstract network model, at the conclusion of the paper a slightly more realistic neuronal implementation of a PEA is outlined based on Izhikevich spiking neurons. Finally, experimental predictions are made for the identification of such informational paths in the brain

Basic science232. Certolizumab pegol prevents pro-inflammatory alterations in endothelial cell function

Background: Cardiovascular disease is a major comorbidity of rheumatoid arthritis (RA) and a leading cause of death. Chronic systemic inflammation involving tumour necrosis factor alpha (TNF) could contribute to endothelial activation and atherogenesis. A number of anti-TNF therapies are in current use for the treatment of RA, including certolizumab pegol (CZP), (Cimzia ®; UCB, Belgium). Anti-TNF therapy has been associated with reduced clinical cardiovascular disease risk and ameliorated vascular function in RA patients. However, the specific effects of TNF inhibitors on endothelial cell function are largely unknown. Our aim was to investigate the mechanisms underpinning CZP effects on TNF-activated human endothelial cells. Methods: Human aortic endothelial cells (HAoECs) were cultured in vitro and exposed to a) TNF alone, b) TNF plus CZP, or c) neither agent. Microarray analysis was used to examine the transcriptional profile of cells treated for 6 hrs and quantitative polymerase chain reaction (qPCR) analysed gene expression at 1, 3, 6 and 24 hrs. NF-κB localization and IκB degradation were investigated using immunocytochemistry, high content analysis and western blotting. Flow cytometry was conducted to detect microparticle release from HAoECs. Results: Transcriptional profiling revealed that while TNF alone had strong effects on endothelial gene expression, TNF and CZP in combination produced a global gene expression pattern similar to untreated control. The two most highly up-regulated genes in response to TNF treatment were adhesion molecules E-selectin and VCAM-1 (q 0.2 compared to control; p > 0.05 compared to TNF alone). The NF-κB pathway was confirmed as a downstream target of TNF-induced HAoEC activation, via nuclear translocation of NF-κB and degradation of IκB, effects which were abolished by treatment with CZP. In addition, flow cytometry detected an increased production of endothelial microparticles in TNF-activated HAoECs, which was prevented by treatment with CZP. Conclusions: We have found at a cellular level that a clinically available TNF inhibitor, CZP reduces the expression of adhesion molecule expression, and prevents TNF-induced activation of the NF-κB pathway. Furthermore, CZP prevents the production of microparticles by activated endothelial cells. This could be central to the prevention of inflammatory environments underlying these conditions and measurement of microparticles has potential as a novel prognostic marker for future cardiovascular events in this patient group. Disclosure statement: Y.A. received a research grant from UCB. I.B. received a research grant from UCB. S.H. received a research grant from UCB. All other authors have declared no conflicts of interes

The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy

Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations. Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves. Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p  90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score. Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care